1. Field of the Invention
This invention relates to a semiconductor laser, and more particularly to compositions of semiconductor layers of a semiconductor laser.
2. Description of the Related Art
As semiconductor lasers emitting a laser beam of a wavelength of 0.98 .mu.m-band, there has been proposed as described, for instance, in "Appl. Phys. Lett., 62(1993)1644" those comprising an n-InGaP clad layer, an In.sub.x3 Ga.sub.1-x3 As.sub.1-y3 P.sub.y3 optical waveguide layer, a GaAs.sub.1-y2 P.sub.y2 tensile strain barrier layer, an In.sub.x1 Ga.sub.1-x1 As compressive strain quantum well layer, a GaAs.sub.1-y2 P.sub.y2 tensile strain barrier layer, an In.sub.x3 Ga.sub.1-x3 As.sub.1-y3 P.sub.y3 optical waveguide layer, a p-InGaP clad layer and a p-GaAs capping layer formed on an n-GaAs substrate.
However this structure is disadvantageous in the following points. That is, in crystal growth by MOCVD (metal organic chemical vapor deposition) method, a rapid substitution of As on P takes place upon switching of hydrogenated V group gases (PH.sub.3, AsH.sub.3) in the course of growth of the tensile strain barrier layer on the optical waveguide layer or growth reverse thereto, which makes unstable the state of the crystal faces. Accordingly it is impossible to generate the interfaces at a high quality with a stable reproducibility and the quality of crystals grown on the interfaces deteriorates.
Further as semiconductor lasers emitting a laser beam of a wavelength of 0.6 to 0.7 .mu.m, there have been widely known those comprising an n-InGaAlP clad layer, an i-InGaAlP optical waveguide layer, a multiquantum well active layer consisting of an InGaAlP barrier layer and an InGaP tensile strain quantum well layer, an i-InGaAlP optical waveguide layer, a p-InGaAlP clad layer and a p-GaAs capping layer formed on an n-GaAs substrate in this order. See, for instance, "IEEE Journal of Selected Topics in Quantum Electronics, Vol.1, No.2(1995)pp.712".
However this structure is disadvantageous in the following points as described in "IEEE Journal of Quantum Electronics, QE-27(1991)pp.1483". That is, growth of InGaP greatly depends upon the orientation on the substrate and the condition of growth and accordingly it is impossible to obtain good crystals with a stable reproducibility. Further since the active layer has tensile strain, high reliability cannot be obtained.
Further in crystal growth by MOCVD (metal organic chemical vapor deposition) method, a rapid substitution of As on P takes place upon switching of hydrogenated V group gases (PH.sub.3, AsH.sub.3) in the course of growth of the clad layer/optical waveguide layer interfaces and the barrier layer/active layer interfaces or growth reverse thereto, which makes unstable the state of the crystal faces. Accordingly it is impossible to generate the interfaces at a high quality with a stable reproducibility and the quality of crystals grown on the interfaces deteriorates.